Medical device with extruded member having helical orientation

ABSTRACT

An elongate polymer member having molecular helical orientation formed by rotation immediately after passing through the extrusion head. The elongate polymer member is rotated downstream of the extrusion head in the molten state prior to solidification in order to impart the molecular helical orientation. Rotating the polymer member in the molten state allows the helical orientation to be imparted at the molecular level, and allows for more rotations per lineal foot of extrusion.

CROSS-REFERENCE OF CO-PENDING APPLICATIONS

[0001] This application is a continuation of U.S. application Ser. No.09/898,710, filed Jul. 3, 2001 and entitled “Medical Device WithExtruded Member Having Helical Orientation.”

FIELD OF THE INVENTION

[0002] The present invention generally relates to medical devices havingextruded polymeric members. More specifically, the present inventionrelates to medical devices such as intravascular catheters and guidewires having extruded polymeric members with helical orientation.

BACKGROUND OF THE INVENTION

[0003] A wide variety of medical devices utilize extruded polymericmembers. For example, intravascular catheters and guide wires commonlyutilize an extruded polymeric member as a shaft component. Becauseintravascular catheters and guide wires must exhibit good torqueability,trackability and pushability, it is desirable that the extrudedpolymeric shaft component have good torque transmission, flexibility andcolumn strength. These attributes are commonly incorporated intointravascular devices by utilizing a composite shaft construction.Alternatively, the polymer material which forms the shaft component maybe oriented to enhance the mechanical characteristics thereof.

[0004] For example, U.S. Pat. No. 5,951,494 to Wang et al. discloses avariety of medical instruments, such as guide wires and catheters,formed at least in part of elongated polymer members having helicalorientation. The helical orientation is established by processing anelongate polymer member with tension, heat and twisting. Wang et al.theorize that the tension, heat and twisting process results in apolymer member that has helical orientation on the molecular level. Suchmolecular helical orientation enhances torque transmission of theelongate polymer member, which is important for some types ofintravascular medical devices that must be navigated through long andtortuous vascular pathways.

[0005] Wang et al. teach that the tension, heat and twisting is apost-processing technique performed on a pre-formed polymer member. Thepre-formed polymer member may comprise, for example, a rod, a tube, apolymer-metal composite, or a polymer/non-metal composite. Because Wanget al. teach post-processing of a pre-formed polymer member, theresulting oriented polymer member inherently involves two (or more)separate processes. First, the polymer member must be formed by, forexample, an extrusion process, and second, the polymer member must beoriented by post-processing (i.e., tension, heat and twisting).

[0006] Because these two separate processes may involve manufacturinginefficiencies, it is desirable to provide a single manufacturingprocess to form an elongate polymer member having helical molecularorientation. For example, it may be desirable to provide an extrusionprocess to obtain a polymer member with molecular helical orientation.However, to our present knowledge, such an extrusion process is notknown in the prior art. Perhaps the closest examples of relatedextrusion processes are disclosed in U.S. Pat. No. 5,059,375 to Lindsayand U.S. Pat. No. 5,639,409 to Van Muiden.

[0007] Lindsay '375 discloses an extrusion process for producingflexible kink resistant tubing having one or more spirally-reinforcedsections. The extruder includes a rotatable head having an extrusionpassageway for spirally extruding a thermoplastic filament into a basethermoplastic material to form a spirally-reinforced tube. The rotatablehead is rotated at a predetermined velocity to form the reinforcementfilament in a spiral or helical pattern in the wall of the tubing.However, with this process, the wall of the tubing is not helicallyoriented at all, and neither the filament nor the wall of the tubing arehelically oriented on the molecular level. Accordingly, the resultingtubing does not enjoy the advantages obtained by molecular helicalorientation as disclosed in Wang et al.

[0008] Van Muiden '409 discloses an extrusion process for manufacturinga tube-like extrusion profile by conveying a number of divided streamsof different polymeric materials to a rotating molding nozzle. Thestreams of material flow together in the rotating molding nozzle to format least two helically shaped bands of material. After allowing thecombined streams of material to cool off, an extrusion profilecomprising a plurality of bands of polymeric material extending in ahelical pattern is formed. However, the bands of material are nothelically oriented on the molecular level as in Wang et al. since thehelical pattern is imparted by the rotating nozzle when the polymericmaterials are in a molten state.

[0009] From the foregoing, those skilled in the art will appreciate thatthere exists an unmet need for a single manufacturing process to form anelongate polymeric member having molecular helical orientation.

SUMMARY OF THE INVENTION

[0010] To address this unmet need, the present invention provides anelongate polymer member having molecular helical orientation formed byrotation immediately after passing through the extrusion head. Inparticular, the elongate polymer member is rotated downstream of theextrusion head in the molten state prior to solidification in order toimpart the molecular helical orientation. The molten state refers to astate in which the polymer is below the melting temperature but abovethe glass transition temperature. Rotating the polymer member in themolten state allows the helical orientation to be imparted at themolecular level. In addition, rotating the polymer member in the moltenstate allows for more rotations per lineal foot than otherwise feasiblewith post-processing techniques.

[0011] The polymer member may be rotated at speeds of 1000 rpm or more,and preferably at 3,500 rpm or more. The extrusion rate may range from10 fpm to 100 fpm, and preferably 20 fpm to 50 fpm. The resultinghelical orientation ranges from 10 rotations per foot (rpf) to 350 rpf,and preferably ranges from 70 rpf to 175 rpf. The extrusion rate and/orthe rotation rate may be varied during the extrusion process to vary thedegree of molecular orientation at various positions along the elongatemember.

[0012] The elongate polymer member may comprise a single polymerextrusion, a multi-polymer intermittent co-extrusion, or a multi-polymercontinuous co-extrusion. The elongate polymer member may comprise asingle layer, multiple layers, or a composite. The elongate polymermember may be extruded over a core member which may carry a substrate(e.g., PTFE tube, wire braid, wire coil, etc.) onto which the elongatepolymer member is extruded. The core member may be removed afterextrusion to form a tubular structure. The elongate polymer member maybe fed back into the extrusion system for a second pass to create anouter layer preferably having a molecular helical orientation in theopposite direction from that of the first pass.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a schematic illustration of an extrusion system inaccordance with an embodiment of the present invention, showing theextrusion head in cross section;

[0014]FIG. 2 schematically illustrates an elongate polymer memberwithout helical orientation;

[0015]FIG. 3A is a cross-sectional view taken along line 3-3 in FIG. 2showing a solid polymer member;

[0016]FIG. 3B is a cross-sectional view taken along line 3-3 in FIG. 2showing a tubular polymer member;

[0017]FIG. 4 schematically illustrates an elongate polymer member withmolecular helical orientation;

[0018]FIG. 5A is a cross-sectional view taken along line 5-5 in FIG. 4showing a solid polymer member;

[0019]FIG. 5B is a cross-sectional view taken along line 5-5 in FIG. 4showing a tubular polymer member;

[0020]FIG. 6 schematically illustrates a longitudinal sectional view ofan elongate polymer member having molecular helical orientation formedby intermittent co-extrusion;

[0021]FIG. 7 schematically illustrates an elongate polymer member havingmolecular helical orientation formed by continuous co-extrusion;

[0022]FIG. 8 illustrates an intravascular balloon catheter incorporatingan extruded polymeric member having molecular helical orientation inaccordance with the present invention; and

[0023]FIG. 9 illustrates an intravascular guide wire incorporating anextruded polymeric member having molecular helical orientation inaccordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0024] The following detailed description should be read with referenceto the drawings in which similar elements in different drawings arenumbered the same. The drawings, which are not necessarily to scale,depict illustrative embodiments and are not intended to limit the scopeof the invention.

[0025] Refer now to FIG. 1 which illustrates an extrusion system 10 inaccordance with the present invention. Extrusion system 10 includes oneor more extruders 12 coupled to a non-rotatable extrusion head 20 asschematically illustrated by extrusion lines 18. Each extruder 12includes a hopper 13, a heated barrel 14, an extrusion screw 15, and acontrol system 16, which may be coupled to other control systems ofother extruders as indicated by dashed line 17 to facilitateco-extrusion.

[0026] Molten polymer enters the extrusion head 20 at inlets 22. Themolten polymer flows through the extrusion passages 24 as indicated bythe small arrows. The molten polymer exists the extrusion head 20through outlet 26. Upon exiting the extrusion head 20 through outlet 26,the molten polymer begins to solidify thereby creating a molten polymerstate. In the molten state, the polymer typically has a temperaturebelow the melting point but at or above the glass transition point.

[0027] In this molten state, the elongate polymer member is rotated asindicated by arrow 30. The elongate polymer member 100 may be rotatedmanually or automatically by a suitable rotational drive mechanism. Thedirection of rotation 30 may be clockwise or counter clockwise asdesired. By rotating the polymer member 100 in the molten state, amolecular helical orientation is imparted thereto. In particular, in themolten state, the crystalline regions of the polymer are helicallyoriented by rotation and subsequently allowed to cool to thereby lock-inthe helical orientation. The molecular helical orientation imparted tothe polymer member 100 is similar to the helical orientation imparted bythe process disclosed in U.S. Pat. No. 5,951,494 to Wang et al., theentire disclosure of which is hereby incorporated by reference.

[0028] The elongate polymer member 100 may be cut into discrete lengthsimmediately after extrusion or spooled onto spool 40. Spool 40 rotatesin a direction indicated by arrow 44 about an axis at the intersectionof lines 42. If the elongate polymer member 100 is taken up by spool 40,the elongate polymer 100 and the spool 40 may be rotated simultaneously.

[0029] The elongate polymer member 100 may be formed by a single polymeror by multiple polymers by co-extrusion. For purposes of illustrationonly, the extrusion system 10 is shown as a two polymer co-extrusionsystem. Those skilled in the art will recognize that the extrusion head20 and the number of extruders 12 may be modified depending on thenumber of polymers incorporated into the elongate polymer member 100.

[0030] The elongate polymer 100 may have a solid cross section or atubular cross section. In addition, the elongate polymer member 100 maybe extruded over a core member 50 which may be left in the elongatepolymer member 100 or subsequently removed. The core member 50 is fedinto the extrusion at 20 by guide tube 28. The core member 50 maycomprise a metal wire or may comprise a composite substrate disposed ona metal wire. Examples of composite substrates include wire braid, wirecoils, polymer braids, polymer coils, lubricious tubular members such asPTFE, etc. Subsequent to extrusion, the core member 50 may be removed toform a tubular elongate polymer member 100, with the substrate (if any)previously disposed on the core member 50 imbedded into the insidesurface of the tubular elongate member 100.

[0031] If a core member 50 is used, the core member 50 is preferablyrotated as indicated by arrow 60. Also preferably, the direction ofrotation 60 of the core member 50 is the same as the direction ofrotation 30 of the elongate polymer member 100. The core member 50 maybe rotated manually or automatically by a suitable drive mechanism. Thecore member 50 may be disposed on spool 70 which rotates in thedirection indicated by arrow 74 about an axis at the intersection oflines 72. If the core member 50 is provided on a spool 70, it may benecessary to rotate the spool 70 along with the core member 50 asindicated by arrow 60.

[0032] As an alternative, the core member 50 may comprise a previouslyformed polymer member 100 having helical orientation. In particular, theelongate polymer member 100 may be fed back into the extrusion system asa core member 50 for a second pass. The second pass creates an outerpolymeric layer having a molecular helical orientation. Preferably, inthe second pass, the elongate polymer member 100 and outer layer arerotated in the opposite direction from that of the first pass to providehelical orientation in different directions.

[0033] Refer now to FIGS. 2 and 4 which provide a schematic comparisonbetween an elongate polymer member 100A without molecular helicalorientation as shown in FIG. 2 and an elongate polymer member 100B withmolecular helical orientation as shown in FIG. 4. The elongate polymermembers 100A/100B are illustrated with longitudinal reference lines 110and radial reference lines 120. Although reference lines 110/120 arevisible on a macroscopic level, it can be appreciated by those skilledin the art that rotation of the polymer member 100 in the semi moltenstate results in molecular helical orientation only visible on themicroscopic level. By comparison, it can be seen that rotation of thepolymer member 100 in the molten state downstream of the extrusion head20 results in a helical orientation of the reference lines 110/120. Bythe cross sectional views shown in FIGS. 4A and 4B, it can beappreciated that the helical orientation extends through the entirecross section of the polymer member 100B.

[0034] The polymer member 100 may be rotated at speeds of 1000 rpm ormore, and preferably at 3,500 rpm or more. The extrusion rate may rangefrom 10 fpm to 100 fpm, and preferably 20 fpm to 50 fpm. The resultinghelical orientation ranges from 10 rotations per foot (rpf) to 350 rpf,and preferably ranges from 70 rpf to 175 rpf. The extrusion rate and/orthe rotation rate may be varied during the extrusion process to vary thedegree of molecular orientation at various positions along the elongatepolymer member 100.

[0035] As mentioned previously, the elongate polymer member 100 maycomprise a single polymer extrusion or a multiple-polymer co-extrusion.FIG. 6 is a longitudinal sectional view of a polymeric tubular member100 formed by intermittent co-extrusion. FIG. 7 is a plan view of apolymeric extrusion member 100 formed by continuous co-extrusion. Asseen in FIG. 6, an intermittent co-extrusion process results in apolymeric extrusion member 100 comprising a first material 102 and asecond material 104 disposed end-to-end, both of which have molecularhelical orientation. With the exception of rotation downstream of theextrusion head, this type of co-extrusion is generally described in U.S.Pat. No. 5,533,985 to Wang, the entire disclosure of which is herebyincorporated by reference. As seen in FIG. 7, a continuous co-extrusionprocess results in a polymeric extrusion member 100 comprising a firstpolymeric material 102 and a second polymeric material 104 forming ahelical band, both of which have molecular helical orientation. With theexception of rotation downstream of the extrusion head, this type ofco-extrusion is generally described in U.S. Pat. No. 5,639,409 to VanMuiden, the entire disclosure of which is hereby incorporated byreference.

[0036] The polymeric extrusion member 100 may be incorporated into awide variety of medical devices such as an intravascular catheter 200illustrated in FIG. 8. Specifically, the elongate polymer member 100having molecular helical orientation may be incorporated into the shaft210 and/or the balloon 220 of the intravascular balloon catheter 200. Ineither case, the extruded polymeric member 100 may comprise a tubularmember having one or more lumens extending therethrough. If incorporatedinto the inflatable balloon 220 of the intravascular balloon catheter200, the polymeric tubular member 100 may comprise the balloon blankwhich is formed into the balloon 220 by a conventional blow-moldingprocess. By incorporating the polymeric extrusion 100 into a cathetershaft 210, the molecular helical orientation improves kink-resistanceand also allows for variable stiffness. By utilizing the polymericmember 100 to form the balloon 220, the molecular helical orientationprovides better puncture resistance and higher burst strength, and mayalso be used to alter the compliance of the balloon 220. By utilizingthe polymeric member 100 to form the balloon sleeve 222, the molecularhelical orientation provides more flexibility such that the sleeveportion 222 behaves similar to the shaft 210, which is particularlybeneficial if relatively stiff balloon materials are used to obtain thedesired balloon performance.

[0037] By way of example, a catheter shaft 210 was made from asingle-layered polymeric tube 100 formed from polyether block amide(PEBAX 7233 SA01) having 30% LCP (LKX1111) mixed therein. The tubing 100was extruded and rotated at 3500 rpm in accordance with the presentinvention to have an inside diameter of 0.018 inches and an outsidediameter 0.023 inches. The resulting shaft 210 exhibited better kinkresistance than that formed without helical orientation. In addition,the helical orientation reduces the brittleness of shaft 210,particularly when high content LCP is used.

[0038] Also by way of example, a balloon 220 was made from amulti-layered polymeric tube 100 having seven layers. The first, third,fifth and seventh layers were formed from polyether block amide (PEBAX7233 SA01), and the second, fourth and sixth layers were formed frompolyether block amide (PEBAX 7233 SA01) having 10% LCP (LKX1111) mixedtherein. The tubing 100 was extruded and rotated at 3500 rpm inaccordance with the present invention to have an inside diameter of0.0175 inches and an outside diameter 0.0345 inches. The extruded tubing100 was blow-molded to form a balloon 220 having an outside diameter of3.0 mm, a length of 20 mm, and a wall thickness of 0.007 inches. Theballoon 220 was tested to have a burst strength of 27198 psi at a burstpressure of 309 psi.

[0039] The polymeric extrusion member 100 may also be incorporated intoan intravascular guide wire 300 illustrated in FIG. 9. The elongatetubular member 100 may comprise a solid cross section to form the shaft310 or a tubular cross section to be disposed about a metallic coremember of the shaft 310. By incorporating the polymeric extrusion 100into a guide wire shaft 310, the molecular helical orientation improveskink-resistance and torque transmission, and also allows for variablestiffness.

[0040] Those skilled in the art will recognize that the presentinvention may be manifested in a variety of forms other than thespecific embodiments described and contemplated herein. Accordingly,departures in form and detail may be made without departing from thescope and spirit of the present invention as described in the appendedclaims.

What is claimed is:
 1. A medical device comprising an elongate polymermember made by an extrusion process including the step of rotating thepolymer member after extrusion but prior to solidification while thepolymer member is still in a molten state to impart a molecular helicalorientation to the polymer member.
 2. A medical device as in claim 1,wherein the elongate polymer member has a surface and a body, andwherein the molecular helical orientation extends through the surfaceand the body.
 3. A medical device as in claim 1, wherein the elongatepolymer member is made by a co-extrusion process of two or moredifferent polymers.
 4. A medical device as in claim 3, wherein theelongate polymer member is made by an intermittent co-extrusion processof two or more different polymers such that a proximal portion of theelongate polymer member comprises a first polymer and a distal portionof the elongate polymer member comprises a second polymer.
 5. A medicaldevice as in claim 3, wherein the elongate polymer member is made by acontinuous co-extrusion process of two or more different polymers suchthat the elongate polymer member comprises two or more coextendinghelically oriented polymers.
 6. A medical device as in claim 1, whereinthe molecular helical orientation comprises 100 rotations per foot ormore.
 7. A medical device as in claim 6, wherein the molecular helicalorientation varies as a function of length of the elongate tubularmember to impart variable flexibility.
 8. A medical device as in claim1, wherein the medical device comprises a guidewire and the elongatepolymer member forms a shaft of the guidewire.
 9. A medical device as inclaim 1, wherein the medical device comprises a catheter and theelongate polymer member forms a tubular shaft of the catheter.
 10. Amedical device as in claim 1, wherein the medical device comprises aballoon catheter and the elongate polymer member forms a balloon of theballoon catheter.
 11. A medical device as in claim 1, wherein themedical device comprises a balloon catheter and the elongate polymermember forms a balloon sleeve of the balloon catheter.
 12. A medicaldevice as in claim 1, wherein the polymer member consists of a polymerhaving a melting temperature and a glass transition temperature.
 13. Amedical device as in claim 1, wherein a first elongate polymer member isa core member of a second elongate polymer member situated around thecore member.
 14. A medical device as in claim 13, wherein the secondelongate polymer member is rotated in a different direction than thefirst elongate polymer member.
 15. A medical device as in claim 1,wherein the medical device comprises a removable core member and theelongate polymer member forms a shaft of the removable core member. 16.A medical device as in claim 15, wherein the core member consists of ametal wire.
 17. A medical device as in claim 15, wherein the core memberconsists of a composite substrate disposed on the metal wire.
 18. Amedical device as in claim 1, wherein the molecular helical orientationis formed by rotation immediately after extrusion thereof.